Non-metallic sprockets and gears have gained wide acceptance in the industry due to the fact that, relative to their metal counterparts, sprockets of the non-metallic type are inexpensive, lightweight and tend to be of silent operation. One exemplary use is as a sprocket to drive a timing belt for internal combustion engines. The non-metallic sprockets do not wear the rubberized or synthetic timing belt as much as with a comparable metal sprocket.
Various techniques are known in the prior art for manufacturing the aforementioned non-metallic sprockets. One method, described in the Guay U.S. Pat. No. 1,501,026 issued July 8, 1924 consists of laminating layers of circular or annular material in the axial direction. The laminations, pre-impregnated with, for example, phenolic resin are then pressed and heated in a mold causing the resin to melt and subsequently cure (i.e., harden) resulting in a sprocket of desired characteristics.
Another method heretofore used for creating a non-metallic sprocket is the mixture of bits of fabric material or the like with a binder, such as for example, phenolic resin, to form a molding compound. This molding compound is thereafter permitted to dry in for example a cylindrical or tablet shape, for later use in the molding process. The resin pre-impregnated molding compound is thereafter placed in a mold with for example a metallic hub whereupon the mold compound is pressed and heated melting the resin and causing the molding compound to properly fill the mold. After the molding compound has cured the mold is opened yielding a non-metallic sprocket consisting of a mixture of fabric and hardened resin surrounding the hub.
To form the requisite teeth in sprockets formed by either of the above methods the mold may have a circumferential tooth imaging die which is filled by the laminates or the molding compound during the molding of the sprocket. Alternately teeth may be hobbed from a molded cylindrical sprocket blank.
It has been found that the teeth of sprockets formed by either of the above methods do not possess the wear characteristics required by many modern applications. For example, in sprockets used to drive timing belts for an automobile, it has been found that advances in the construction of the timing belt resulting in its longer life has, in turn, created additional wear upon the teeth of the sprocket resulting in their premature failure.
It has further been found that the inclusion of a metallic hub substantially increases the overall cost of the sprocket. Substitutes for metallic hubs heretofore used have not proven successful due to the high torques which the hub must withstand in many modern applications.
Therefore, it is an object of the present invention, to set forth a sprocket which overcomes the problems noted above.